Modern aircraft engines require lightweight and highly reliable fuel pumping equipment. A lightweight pump reduces aircraft weight over that of an otherwise identical conventional pump, thereby increasing aircraft range and/or pay load. Moreover, in the usual case, the reduction in the weight of the pump will result in a reduction in it's volume as well. As a consequence, in the usual case a lightweight pump will fit in a smaller envelope which provides the aircraft designer with increased flexibility as well as the ability to progress towards a more slippery aerodynamic design. Consequently, aerodynamic drag may be reduced, further enhancing aircraft performance.
Centrifugal type fuel pumps address many of these demands. Unfortunately, their reliability is somewhat limited due to a relatively short fatigue life of oil-lubricated rolling elements such as ball bearings which must be designed to accommodate the high speeds involved as well as inherent critical speed considerations. Moreover, for obvious reasons, it is necessary to maintain lubricating oil and fuel streams completely separated. Conventionally, this is accomplished through the use of drained cavities within the pump that separate the pumping elements and the lubricated bearings. This in turn translates into the need for complex sealing systems as well as increased size. In the usual case, the axial length of the pump may be increased and the overhung moment is inevitably increased which increases the design complexity.
The present invention is directed to overcoming one or more of the above problems.